#include<iostream>
#include<cmath>
using namespace std;
int main()
{
	int n;
	while (cin >> n)
	{
		bool flag = 1;
		if (n <= 1)
		{
			cout << "no" << endl;
			continue;
		}
		for (int i = 2; i <= sqrt(n); i++)
		{
			if (n % i == 0)
			{
				flag = 0;
				break;
			}
		}
		if (flag == 0) cout << "no" << endl;
		else cout << "yes" << endl;
	}
	return 0;
}